Digital lighting technologies, i.e. illumination based on semiconductor light sources, such as light-emitting diodes (LEDs), offer a viable alternative to traditional fluorescent, HID, and incandescent lamps. Functional advantages and benefits of LEDs include high energy conversion and optical efficiency, durability, lower operating costs, and many others. Recent advances in LED technology have provided efficient and robust full-spectrum lighting sources that enable a variety of lighting effects in many applications. Some of the fixtures embodying these sources feature a lighting module, including one or more LEDs capable of producing different colors, e.g. red, green, and blue, as well as a processor for independently controlling the output of the LEDs in order to generate a variety of colors and color-changing lighting effects, for example, as discussed in detail in U.S. Pat. Nos. 6,016,038 and 6,211,626, incorporated herein by reference.
Multi-chip LEDs (LED packages containing multiple LED chips) provide relatively high levels of light output. However, efficient mixing of the light output from the various LED chips of a multi-chip LED is necessary in order to minimize undesirable visible artifacts, such as color rings/color banding that may be visible around the edge of the beam pattern outputted by the multi-chip LED. Current methodologies employed to mix the light output from the various LED chips of the multi-chip LED involve texturing and/or an elongated compound parabolic concentrator (CPC). Texturing involves the addition of texture on an optic surface in order to scatter light passing through the textured optic surface. Texturing may allow for satisfactory color-mixing in the central area of a beam pattern, but the edges of the beam pattern still often show color rings/color banding. Moreover, the addition of texture to an optical surface typically increases the beam angle of the light output to an unsatisfactory degree and texturing is very hard to maintain and control in production. The use of a CPC may provide satisfactory mixing of the light output from a multi-chip LED, but may also increase the beam angle of the light output to an unsatisfactory degree.
Thus, there is a need in the art to satisfactorily mix the light output from a multi-chip LED package while maintaining a desirable beam angle and efficient package size.